- Antibacterial activity
- Bacteriostatic at all concentrations.
- Gram negative AND some gram positives. (and non-bacterial microbes)
- Aerobes AND anaerobes
- Bacterial resistance
- Limits clinical usefulness for many pathogens.
- More organisms are susceptible to members with high lipid solubility.
- Concentrations and doses
- Lipid solubility (all members) favors good tissue distribution.
- Highly lipid soluble members of the class can be effective for infections in reserved spaces.
- Toxicity Profile
- Life-threatening adverse effects are rare.
- Rapid intravenous administration problematic.
- IV doxycycline should be avoided in horses.>
- Make certain doxycycline oral tablets and capsules are swallowed whole!
- oxytetracycline, tetracycline, chlortetracycline, doxycycline, minocycline
- Bacteriostatic therapy - especially intracellular infections
- Broad antibacterial spectrum
- Rickettsial and chlamydophila infections
- Intracellular infections and in reserved spaces (especially doxycycline and minocycline)
Beneficial actions and effects
- Bacteriostatic at all concentrations (not capable of cidal action)
- Binding to 30s ribosome
- Arrested protein synthesis without misreading of codon
Resistance (by bacteria)
- enzymatic alteration followed by efflux of metabolite
- increased efflux WITHOUT enzymatic alteration does not confer resistance
- GI flora alterations (especially horses)
- Esophageal lesions (doxycycline stuck in esophagus)
- Interfere with bone and tooth development (young animals, fetus)
- Renal tubular necrosis with HIGH DOSE LONG DURATION therapy
- Toxic hepatitis (older agents in people)
- Photosensitivity (rare - perhaps higher with doxycycline)
- Cardiovascular effects with IV administration (may also be vehicle)
- Intravenous doxycycline has been fatal in horses.
Although there are no (formal) subclasses of tetracyclines, there is natural grouping based on lipid solubility. Older tetracyclines (oxytetracycline, tetracycline, chlortetracycline) have the lowest lipid solubility. Doxycycline is intermediate and minocycline is the most lipid soluble. This MOSTLY affects the likelihood that the drug will reach the bacteria in adequate concentration. This is especially important for intracellular infections but it may also be important for antibacterial treatment in reserved spaces (e.g., prostatitis).
- Oral absorption is relatively good for all tetracyclines
- Doxycycline and minocycline reach higher intracellular concentrations
- Doxycycline and minocycline reach reserved spaces
- Injectable dose forms of all tetracyclines can be problematic.
- High concentration forms of oxytetracycline do extend duration but they are not really "long-acting." Pharmacokinetics of absorption and elimination are fairly much unchanged from other dose forms but much larger doses can be given without tissue damage or residues.
- Doxycycline for injection is not recommended for horses
- Tetracycline dose forms for birds (Chlamidophylia psittici infections) are problematic.
- most available products (among the tetracyclines)
- multiple injectable dose forms
- LA products really better tolerated dose forms (larger dose / volume)
- limited injectable forms
- almost exclusively feed and water administration
- will sick animals consume adequate doses?
- injectable forms not particularly suitable
- injectable form used in europe for pet birds not available in US
- muscle damage in pet birds
- iv use not recommended in horses
- most lipid soluble of the class
- should be preferred (among tetracyclines) for intracellular and reserved space infections
- substitute for doxycycline in some therapies depending on price and availability